Periodic Seeding -60- 



Langmuir, in analyzing the data thus obtained, observed that it would 

 be difficult to determine cause and effect. In other words, it would be dif- 

 ficult to know whether the periodicity in weather was caused by periodic 

 seeding or vice versa. For commercial seeding organizations do not seed 

 at any random time but rather choose for seeding those days when weather 

 conditions are propitious. If the conditions are "good" for the production 

 of rain, the operator seeds. As a result, although it might rain naturally, 

 the seeding may increase the quantity of rain- -and it may produce rain 

 when none would have fallen naturally. On the other hand, if conditions 

 are not right for rain, the operator does not seed, for seeding will not pro- 

 duce rain except when meteorological conditions are suitable. 



Meanwhile F. H. Hawkins, Jr., of the U. S. Weather Bureau, in the May 

 1952 issue of the Monthly Weather Review , called attention to the same per- 

 iodicity and stated that, as far as could be determined, no seeding which was 

 under way that spring could compare in periodicity with the marked spacing 

 of rainfall at that time. 



Langmuir, however, examined the data on western seeding operations 

 and was able to show that the observed periodicity in weather conditions co- 

 incided with the schedule of commercial operations. He reported his findings 

 to this effect at the annual meeting of the Institute of Mathematical Statistics 

 in East Lansing, Michigan, on September 4, 1952. 





